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Toshiba T3 PLC Computer Link <-> RS-485 (real time data extraction)

Toshiba T3 PLC Computer Link <-> RS-485 (real time data extraction)

Toshiba T3 PLC Computer Link <-> RS-485 (real time data extraction)


Hi everyone,

I need to interface an external PC with a Toshiba T3 CPU (model PU326H) in order to read data from several 'F' registers.

The external PC sends data via RS-232 to a RS-232 <-> RS-485 converter, then that converter sends data via RS-485 to the Toshiba T3 PLC "Computer Link" port, located on the bottom of the Toshiba T3 PLC.

The setup I have enabled so far is as follows:

Select System Parameters
Inside Computer Link Setup, choose the station (=1)
Inside Computer Link Setup / Communication Parameter choose Baud rate = 19200, Parity=None, 8 data bits, 1 stop bit

See full setup visible from attachment file (PDF).


The problem I am having is that while I can send data via the RS-232 converter, no data is sent back from the Toshiba PLC.

Has anyone ever setup the Computer Link port on a Toshiba T3 PLC? Any clues as to what is causing the issue I am observing?

Any help is appreciated, thank you.

Regards to Eng Tips members.

RE: Toshiba T3 PLC Computer Link <-> RS-485 (real time data extraction)

I have no experience directly with the Toshiba units but I'd do the following:
  • Find out if there's an option (unless this is already what you're doing) for communicating with the port via the Toshiba software
  • Double check the datasheet for any unusual pinouts or connections at either end - this is based on experiences with Omron serial ports, it wouldn't surprise me if Toshiba did the same
  • Confirm that the software is working and that communication can be established with the serial port arrangement (possibly via programming or another port if possible)
It can often get challenging to get things working the first time, and there are at least 3 different devices (PC Serial Port, 232-485 converter, PLC) in the chain, all of which may affect the result. I'm assuming you've not succeeded previously in getting this to work, the approach in faultfinding when it worked previously can be different.

Lastly, RS485 is typically 2 wire, but 4 wires are connected. THe CRO shot tends to indicate the signal is ok, but a double check of the appropriate wiring and possible termination resistor requirement wouldn't go astray. Same with the DIP switches for the converter. RX and TX may also need to be bridged.

RE: Toshiba T3 PLC Computer Link <-> RS-485 (real time data extraction)

Hi FreddyNurk,

Thank you for your input. I think the Computer Link port accepts connection from the Toshiba software (T-PDS), so I should try that at the next opportunity. Pinout-wise I have checked multiples times the wiring, so I am fairly confident I am on the right track there. The whole PC <-> serial port <-> RS-232 to/from RS-485 chain is working fine until data is made available to the Toshiba PLC (that's the oscilloscope screenshot). I also checked already the DIP switches and tried several combinations (amongst them whether to use 120 Ohms termination resistor + 1.2 kOhms transmit/receive bias) to no avail.

Would you know where I could find out the latest version of the Toshiba PLC firmware? Just wondering whether the firmware used (v1.16) is recent or not. The production line is about 20 years old, and I am not clear on whether the firmware was ever updated by anyone.

Does the Toshiba website lists latest firmware available somewhere?

RE: Toshiba T3 PLC Computer Link <-> RS-485 (real time data extraction)

I don't know about whether firmware is available for the unit, but its quite unlikely that its the reason for lack of communications.

I'd double check the 2 wire mode for the RS485, failing that, I'd double check the settings for the port in the PLC if you have access to the code, and can use the RS232 port to communicate, just in case the port has been configured in the code.

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